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      20 November 2019, Volume 47 Issue 11 Previous Issue    Next Issue
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    Additive Manufacturing & Remanufacturing Column
    Research progress in stress and deformation control in laser additive manufacturing for high-performance metals
    Yong CHEN, Hui CHEN, Yi-shuai JIANG, Qian WANG, Ying WU, Jun XIONG, Shi-yun DONG
    2019, 47 (11): 1-10.   DOI: 10.11868/j.issn.1001-4381.2018.001430
    Abstract ( 1278 ( PDF (2235KB)( 724 Citation

    With the development of basic theoretical research and equipment, laser additive manufacturing technology is widely used in the manufacture of large complex components. However, the internal stress in laser additive manufacturing process tends to result in distortion and cracking. Stress and deformation control has become an urgent issue in laser additive manufacturing process. In this paper, research progress of residual stress in laser additive manufacturing was reviewed from various aspects such as residual stress forming mechanism, test methods, control measures. Furthermore, the main problems and research directions were proposed for the research of stress and deformation control technology, which provides guidance for the research of "shape control" in laser additive manufacturing.

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    4D printing and its key technologies
    Zi-cai SHEN, Yan XIA, Yi-gang DING, Chun-qing ZHAO, Yan-bin YANG
    2019, 47 (11): 11-18.   DOI: 10.11868/j.issn.1001-4381.2018.000610
    Abstract ( 1298 ( PDF (1567KB)( 498 Citation

    4D printing can be defined as the evolution of 3D printing structure in terms of shape, performance and function. It has time dependence, printer independence and predictability, and its smart dynamic performance creates promising capabilities and broad potential applications. On the basis of a brief review of the status of 4D printing at home and abroad, the concept and components of 4D printing were given firstly. Then the 4D printing was classified from the dimension of printing structure shape change. Furthermore, the key technologies such as printing materials, incentive mechanism and mathematical modeling method in 4D printing elements were analyzed. Finally, it was pointed out that the development direction of 4D printing technology is to combine intelligent materials with 3D printing, simplify the manufacture of complex structures, and realize the automation, intellectualization and personalization applications in special service environments and fields such as aerospace, deep sea and precise medical treatment by using its unique characteristics of self-assembly, self-adaption and self-repairing.

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    Research progress in 3D printing technology for carbon nanotubes composites
    Hao LU, Nan LI, Hai-bo WANG, Bang-quan LIAO, Ya-ming JIANG, Miao-lei JING, Zhi-wei XU, Li CHEN, Xing-xiang ZHANG
    2019, 47 (11): 19-31.   DOI: 10.11868/j.issn.1001-4381.2018.001239
    Abstract ( 1426 ( PDF (2266KB)( 635 Citation

    3D printing technology is one of the additive manufacturing technologies for rapid process and manufacture of complex geometric components. Based on the three-dimensional data model, the material is accumulated layer by layer controlled by computer, and eventually forms the solid object. Compared to the traditional manufacturing methods, 3D printing technology has many advantages, such as time saving, low cost, easy operation, no mold and strong controllability of component geometry, etc. Along with the development of this technology, several types of 3D printing technologies, such as fused deposition modeling, selective laser sintering, stereo lithography, digital light processing and solvent casting molding, have been produced according to the core of the printing technology, applicable materials and equipment composition. The principles and characteristics of the four most representative 3D printing forming processes were introduced in this paper, and the research progress of carbon nanotubes to reinforce polymer composites with different types of 3D printing forming processes applied in recent years was summarized. At the same time, it was predicted that the 3D printing molding technology will be developed towards the direction of high precision, industrialization, popularization and high integration in this field, and the research and development of 3D printing materials will also have more prospects.

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    Research progress in aluminum alloy additive manufacturing
    Qing-wei GAO, Jian ZHAO, Feng-yuan SHU, Cheng-cheng LYU, Bao-liang QI, Zhi-shui YU
    2019, 47 (11): 32-42.   DOI: 10.11868/j.issn.1001-4381.2019.000084
    Abstract ( 1268 ( PDF (5388KB)( 791 Citation

    Aluminum alloy is the preferred material for lightweight structure, and has broad application prospects in aerospace, transportation and ships. The additive manufacturing of aluminum alloy possesses outstanding advantages and potential on fabricating complicated three-dimensional precision structural parts. Furthermore, this method can be characterized by its high efficiency and excellent structural properties. With regard to the rapid development of the aluminum alloy additive manufacturing, the research status and latest achievements of aluminum alloy fabricated with additive manufacturing from the aspects of structure and performance, precision and quality, controlling of defects and numerical simulation, and the shortcomings of current research were summarized. Based on these, the key issues that will be focused were summarized at last, including realizing the control of the micro-structure, clarifying the forming mechanism of the stress, improving the forming accuracy, and studying the distribution law of the temperature field in the forming process.

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    Current status and development trend of laser remanufacturing of short stress path rolling mill
    Bin ZHANG, Sui-yuan CHEN, Jing LIANG, Chang-sheng LIU, Tong CUI, Mei WANG
    2019, 47 (11): 43-52.   DOI: 10.11868/j.issn.1001-4381.2018.001149
    Abstract ( 541 ( PDF (2560KB)( 236 Citation

    The short-stress-path rolling mill is a mechatronics equipment which is widely used in the steel manufacturing industry. China has the largest number of used rolling mills in the world. Most of the rolling mills are served under the harsh environment of high temperature, high humidity and fretting wear, which leads to the decrease of rolling mill system accuracy and failure scrap. At the same time, the rolling mills in the scrapped state occupy a large amount of storage spaces and site resources of the factories. Furthermore, the natural corrosion of the idle rolling mill will cause serious environmental pollution. Laser remanufacturing is a new type of technology for high-efficiency green rolling mill repairing and remanufacturing. The main failure modes of short-stress-path rolling mills and the application of laser remanufacturing technology on short-stress-path rolling mills were summarized in this paper. From the aspects of mill condition analysis, failure mechanism and material design, the main problems in laser remanufacturing of short-stress-path rolling mill and related research work and latest developments on these issues were reviewed. On this basis, it was pointed out that the main development direction in the future is to design special materials for laser remanufacturing of rolling mill, develop real-time monitoring and feedback system for laser remanufacturing process, and establish evaluation standards for service performance of rolling mill after laser remanufacturing, and to expand the field of laser remanufacturing of rolling mill.

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    Cold spraying hybrid processing technology and its application
    Wen-ya LI, Cong-cong CAO, Xia-wei YANG, Ya-xin XU
    2019, 47 (11): 53-63.   DOI: 10.11868/j.issn.1001-4381.2019.000262
    Abstract ( 836 ( PDF (2779KB)( 437 Citation

    Cold spraying(CS) is a solid-state rapid forming technology, and it has been used in additive manufacturing and repairing damaged aerospace parts. However, the inherent characteristic of cold sprayed deposits, i.e. high strength and low plasticity, limits its industrial applications.The new progress and application about cold spraying hybrid other processing technologies were reviewed in this paper, focusing on the following:cold spraying can not only hybridize with general manufacturing technologies, such as machining and shot peening, but also with the hot working and manufacturing technologies, such as laser, heat treatment, hot rolling, hot isostatic pressing, friction stir processing, friction stir welding and brazing, in order to improve the strength and plasticity of the cold sprayed deposits. The strength and plasticity of the cold sprayed deposits can be improved, and the coatings deposited by cold spraying can promote the weld of nonferrous metals. At last, it should be pointed out that further coordination of cold spraying with various machining processes and cold spraying hybrid welding technology needs to be paid more attention, aiming to expand the connotation of the conventional manufacturing.

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    Research progress in sensitive membrane materials and adsorption mechanism of VOCs sensors
    Xiao-qun SHEN, Li CHEN, Shun-bo LI, Yi XU
    2019, 47 (11): 64-70.   DOI: 10.11868/j.issn.1001-4381.2018.001136
    Abstract ( 712 ( PDF (1670KB)( 403 Citation

    Sensitive membranes that selectively adsorb VOCs (volatile organic compounds) are the key components of VOCs sensors, and sensors' response performance depends on membranes materials and preparation methods. The chemical composition, preparation methods and structural characteristics of sensing membranes materials of VOCs sensors were reviewed, including polymers, inorganics, supermolecules and composite materials, adsorption properties and mechanism of sensitive membrane materials for VOCs were compared and analyzed, especially the recent development of new material-metal-organic frameworks (MOFs) used in VOCs sensors. Finally, challenges and perspectives of sensitive membrane materials in VOCs sensors were also discussed and forecasted, including performance issues of sensors such as sensitivity, cross-response, lifetime, and research of sensitive materials with high porosity and large specific surface area is expected to solve these challenges.

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    Research progress of polymer electrolytes in supercapacitors
    Zhi-yu XUN, Pu HOU, Yang LIU, Shou-peng NI, Peng-fei HUO
    2019, 47 (11): 71-83.   DOI: 10.11868/j.issn.1001-4381.2019.000346
    Abstract ( 785 ( PDF (5418KB)( 557 Citation

    With the rapid development of portable devices, polymer electrolytes with high safety performance are receiving widespread attention. The polymer electrolytes applied in supercapacitors in recent years were introduced in this review, including all-solid-state polymer electrolytes, gel polymer electrolytes, porous polymer electrolytes, composite polymer electrolytes and redox polymer electrolytes capable of providing pseudocapacitance, and the characteristics and research progress were also discussed in details. It was proposed that the development of organic composite gel polymer electrolytes with wide voltage window, high ionic conductivity, high mechanical strength and light weight will be the trend in the field of electrolytes for supercapacitors in the future. Polymer electrolyte with excellent comprehensive performance will play an important role in the field of new energy resources such as supercapacitors.

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    Research Article
    Experimental/numerical investigation of moisture diffusion in glass/epoxy composites in consideration of interlamination and interphase
    Li-bao ZHU, Wen-xi DAI, Yong-qing LI, Xi ZHU, Zi-xu ZHU
    2019, 47 (11): 84-91.   DOI: 10.11868/j.issn.1001-4381.2019.000016
    Abstract ( 574 ( PDF (2980KB)( 229 Citation

    In order to investigate the influence of the composite interlamination and interphase on the moisture absorption diffusivity, moisture absorption experiments were conducted on both unidirectional glass/epoxy composite and pure epoxy resin and the composite three dimensional diffusivities were obtained. The composite interlamination and interphase were observed by optical microscope and atomic force microscope, separately. Based on the experimental results, the composite transient diffusion finite element (FE) models and steady diffusion FE models were established, taking account of interlamination and interphase. Results show that the composite diffusivity along the fiber direction is larger than that in the direction transverse to the fiber. Diffusivities of the two directions transverse to the fiber were different. FE models with interlamination can more realistically reflect the composite structure and its moisture absorption process. Interlamination promotes diffusion in the direction transverse to fiber and warp affects the diffusivity apparently. The orthotropic interphase properties need to be considered to fit the three dimensional composite diffusivities.

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    Tribological behavior and wear mechanism of modified nano-SiO2 reinforced epoxy composites
    Jin TIAN, Li GAO, Bin CAI, Ze-hao QI, Ye-fa TAN
    2019, 47 (11): 92-99.   DOI: 10.11868/j.issn.1001-4381.2018.001293
    Abstract ( 556 ( PDF (4786KB)( 186 Citation

    Nano-SiO2 surface grafted APTES (T-SiO2) was realized by covalent functionalization technology, and functionalized nano-SiO2 modified epoxy resin composite (T-SiO2/EP) was prepared. The surface functional groups and chemical elements of the functionalized nano-SiO2were analyzed and the mechanical and tribological properties of the T-SiO2/EP were tested. The results show that the mechanical and tribological properties of the epoxy resin are effectively improved due to the introduction of functionalized nano-SiO2. When the content of functionalized nano-SiO2 is 2%(mass fraction, same as below), the microhardness and fracture toughness of the composites (2%T-SiO2/EP) can reach the maximum, which are 70.2HD and 1.02MPa·m1/2 respectively, moreover, in dry friction condition, the friction coefficient and the wear loss reach the minimum, which are 0.49mg and 1.7mg respectively. Compared with pure epoxy resin, they are reduced by 31.9% and 34.6%, and compared with 2% unmodified nano-SiO2 reinforced epoxy resin composite, they are reduced by 14% and 10.5%, and the corresponding wear mechanism is analyzed.

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    Viscosity-controllable preparation and characterization of BPDA-PDA polyimide
    Hong-jiang NI, Yu XING, Xiao-xiang DAI, Jun LI, Dai-jun ZHANG, Shi-yong YANG, Xiang-bao CHEN
    2019, 47 (11): 100-106.   DOI: 10.11868/j.issn.1001-4381.2019.000146
    Abstract ( 768 ( PDF (1891KB)( 312 Citation

    With precursor modification by regulating dianhydride hydrolysis degree, the viscosity of polyimide precursor solution, derived from 3, 3', 4, 4'-biphenyl tetracarboxylic dianhydride (BPDA) and para-phenylenediamine (PDA), was facilely manipulated. The chemical structure of the precursor was characterized by infrared (IR) spectrometry and proton nuclear magnetic resonance (1H-NMR) spectrometry. The effects of dianhydride hydrolysis on the viscosity, imidization process and properties were investigated. The results show that the precursor can be formed from hydrolytic BPDA and PDA, with amide acid and carboxylic ammonium salt groups in the molecular structure. The viscosity of the precursor can be reduced by the introduction of carboxylic ammonium salt group, achieving the effective regulation of viscosity in the 10-105cP range. Importantly, the existence of carboxylic ammonium salt shows no influence on the complete imidization of the precursor, which guarantees the maintenance of mechanical property. Interestingly, the coefficient of thermal expansion (CTE) of this BPDA-PDA polyimide films can be reduced by this viscosity manipulation method.

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    Modification and hydrogen evolution characteristics of post-processing PtCu/C alloy solid solubility gradient membrane catalyst
    Bai-guang WEI, Xin-yu HAO
    2019, 47 (11): 107-114.   DOI: 10.11868/j.issn.1001-4381.2018.001256
    Abstract ( 568 ( PDF (4935KB)( 195 Citation

    PtCu/C membrane catalysts were prepared by ion beam sputtering (IBS) with moving bimetallic Pt and Cu targets. The surface structure of the catalyst with large specific surface area was obtained by surface etching of the gradient membrane with 1mol/L HNO3. The results of X-ray diffraction (XRD) analysis show that the PtCu replacement solid solution alloy is formed on the surface of the composite membrane electrode, the original Pt lattice is contracted and the spacing between the crystal planes is narrowed. Atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM) RTEM-STEM measurements show that the surface of the post-processed samples has multi-peak structure and trench-pore structure. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used to test the electrochemical hydrogen evolution performance of the samples. The results show that the dealloying of gradient materials can effectively reduce the platinum loading and improve the exchange current density of electrochemical hydrogen evolution. The Pt loading of the post-treatment sample is decreased by 20.29%, the exchange current density of electrochemical hydrogen evolution reaches 0.004217A/cm2, and the catalytic performance is improved by 20.58%.

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    High performance MnO2@Ni(OH)2 core/shell structure nanowire arrays supported on carbon cloth as advanced electrodes for asymmetric supercapacitors
    Hui-jun YAN, Jian-wei BAI, Yu WANG, Hong-xia ZHOU, Xiao-yan JING, Jun WANG, Xue-feng BAI
    2019, 47 (11): 115-122.   DOI: 10.11868/j.issn.1001-4381.2018.000971
    Abstract ( 558 ( PDF (5544KB)( 270 Citation

    MnO2@Ni(OH)2 core/shell structure nanowire arrays (NWAs) supported on carbon cloth were successfully synthesized by a two-step method, applied in flexible all-solid-state asymmetric supercapacitors (ASCs). The Ni(OH)2 nanosheets wrapped on the surface of each MnO2 nanowire uniformly, which can increase the capacitance of MnO2 NWAs to a high specific capacitance of 432.8F/g at 5mV/s. The electrode also exhibits good cycling ability, 92.3% of the initial capacity can be remained after 2000 cycles at 5A/g. The assembled MnO2@Ni(OH)2//MnO2 asymmetric device with a maximum voltage of 1.8V has been fabricated, delivering both high energy density (69.2Wh/kg) and power density (4.5kW/kg at 54.6Wh/kg). These results show that MnO2@Ni(OH)2 NWAs with large specific surface area, combined with the flexible carbon cloth substrate can be applied in supercapacitor field in large scale.

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    Density functional theory study of Ba2+ adsorption on KDP (100) surface
    Yao LIU, Yu-lin WU, Yun-peng QU, Wen-ying GUO, Li-ping LIANG
    2019, 47 (11): 123-127.   DOI: 10.11868/j.issn.1001-4381.2018.001028
    Abstract ( 521 ( PDF (1590KB)( 162 Citation

    In order to study the nature of interaction between Ba2+ and the KDP crystal surface, the adsorption behavior of Ba2+ on the KDP (100) surface was calculated by using density functional theory (DFT). The results show that the adsorption energies of Ba2+ on the KDP (100) surface are negative, indicating the adsorption processes are spontaneous and exothermic. Three types of adsorption configurations are formed after structure optimizations, and final adsorption positions are top sites on O atoms or bridge sites between two O atoms. The most stable adsorption system can be observed when Ba2+ on the bridge site between two O atoms within a phosphate group. In the three different adsorption configurations, Ba2+ can form ionic bonds with the surface O atoms, while interactions between Ba2+ and the surface H atoms exhibit covalent character. The P-O, H-O, and K-O bonds on the KDP (100) surface are elongated or shortened after Ba2+ adsorption, and the structure of hydrogen bonds on the surface also have been changed significantly.

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    g-C3N4 quantum dots decorated spherical Bi2WO6 photocatalyst and its enhanced photocatalytic activities mechanism
    Li GUO, Kai-lai ZHANG, Xin ZHANG, Fang-li ZHAO, Qiang ZHAO, Xiao YANG, Dan-jun WANG, Feng FU
    2019, 47 (11): 128-134.   DOI: 10.11868/j.issn.1001-4381.2018.000459
    Abstract ( 611 ( PDF (4727KB)( 220 Citation

    Three-dimensional(3D) Bi2WO6 architecture was successfully synthesized via a hydr-othermal process. The g-C3N4 quantum dots(QDs) were deposited on the surface of as-synthesized 3D Bi2WO6 hierarchical structure to construct the novel Z-scheme g-C3N4/Bi2WO6 heterojunctions via a simple impregnation-calcination method. The morphology, composition and visible-absorptive properties of as-synthesized samples were characterized by XRD, FE-SEM, TEM, UV-Vis-DRS techniques. Methylene blue(MB) and p-nitrophenol(p-NPh) were selected as model pollutant to investigate the effect of g-C3N4 QDs on the photocataytic activity of Bi2WO6 nanoarchitecture. The results reveal that as-prepared Bi2WO6 exhibits the 3D architecture with the pore size of about 10nm via a simple impregnation-calcination method. g-C3N4 QDs with the size of about 5nm can be deposited on the surface of secondary nanoplate of Bi2WO6. The photocatalytic activity of Z-scheme g-C3N4/Bi2WO6 is superior to the pure g-C3N4 and Bi2WO6, and 10%g-C3N4/Bi2WO6 exhibits the best photocatalytic activity for MB and p-NPh. The apparent rate constant (kapp) for the degradation of MB is as high as 4.5 and 5.8 times, 2.6 and 1.6 times for p-NPh compared to that of pure g-C3N4 and Bi2WO6, respectively. The O2·- is the main reactive species during the photocatalytic process. The catalytic efficiency enhancement of g-C3N4/Bi2WO6 relative to Bi2WO6 or g-C3N4 can be attributed to the formation of heterojunction between g-C3N4 QDs and Bi2WO6, which suppresses the recombination of photogenerated electron/hole pairs as well as broaden the light absorption.

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    Effects of sintering temperature on W-Mo-Cu alloy prepared by large current electric field sintering
    Yan-fang LIU, Ke-qin FENG, Hong-ling ZHOU, Si-xuan KE
    2019, 47 (11): 135-140.   DOI: 10.11868/j.issn.1001-4381.2018.001160
    Abstract ( 502 ( PDF (3214KB)( 156 Citation

    The W-Mo-Cu alloy was rapidly prepared by a large current electric field sintering method at 875-1000℃. Effect of sintering temperature on microstructure, hardness and electrical conductivity was investigated. Based on the dimensional change during alloy sintering, the sintering characteristic index was obtained by fitting calculation, and the main migration mechanism of W-Mo-Cu alloy during sintering was inferred. The results show that the pores of the W-Mo-Cu alloy decrease, the relative density, microhardness and electrical conductivity increase at the same time with the increase of sintering temperature at 875-975℃. When the sintering temperature is between 875℃ and 925℃, the densification of the alloy is mainly caused by plastic deformation instead of sintering; when the sintering temperature is higher than 925℃, the order of the main migration mechanism experienced during the densification of W-Mo-Cu alloy is plastic flow, volume diffusion, grain boundary diffusion and surface diffusion.

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    Corrosion and slurry erosion properties of FeCrNiCoCuAlx high-entropy alloy coatings prepared by laser cladding
    Ya-yun BAO, Xiu-lin JI, Cui-cui JI, Jian-hua ZHAO, Jiang-bo CHENG, Lin XU
    2019, 47 (11): 141-147.   DOI: 10.11868/j.issn.1001-4381.2018.000065
    Abstract ( 778 ( PDF (2657KB)( 359 Citation

    FeCrNiCoCuAlx (x=0, 1, 2, 3) high-entropy alloy (HEA) coatings were prepared on Q345 steel by laser cladding. The effects of Al content on microstructure and properties of FeCrNiCoCuAlx HEA coatings were studied by XRD, SEM and erosion wear tests. The results show that the HEA coatings are mainly composed by simple FCC and BCC solid-solution phases. With the increase of Al addition, the microstructure is evolved gradually from FCC to BCC. And the hardness of the HEA coatings improves significantly and the maximum value is 580HV. In 3.5%NaCl solution, the corrosion current density of FeCrNiCoCuAlx HEA coatings decreases firstly and then increases with the increase of Al addition. And the HEA coating has the best corrosion resistance at x=1. Meanwhile, the mass loss rate of HEA coating decreases in the erosion test when the impact angle is changed from 90° to 30°, exhibiting an erosion characteristic of ductile materials. The slurry erosion properties of the HEA coating increase with the increase of Al content, and the erosion wear mechanism is evolved from forging extrusion to ploughing and micro-cutting.

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    Preparation and research of structure-gradient and corrosion-resistant aluminium coatings on steel surface
    Yao WANG, Xue-ni ZHAO, Xin-an DANG, Pu YANG, Sen-sen WEI, Wei-gang ZHANG, Qing-yao LIU
    2019, 47 (11): 148-154.   DOI: 10.11868/j.issn.1001-4381.2018.001128
    Abstract ( 457 ( PDF (4949KB)( 229 Citation

    In order to control the composition and microstructure of corrosion-resistant aluminum coatings, a layer of pre-coating was deposited on Q235 steel surface by magnetron sputtering, and then corrosion-resistant aluminum coating with a certain thickness was prepared by hot dipping. Microstructure, thickness and chemical composition of aluminum coating were characterized by SEM equipped with EDS. The bonding strength of aluminum coating to substrate was tested by scratch test, and corrosion resistance was evaluated by salt water corrosion test. The results show that the coating obtained by magnetron sputtering combining with hot dipping is relatively denser. The aluminum coating prepared by both hot dipping and magnetron sputtering combining with hot dipping consists of an outer Al layer and an inner Fe-Al alloy layer. The thicknesses of Al layers are (45.75±6.41) μm and (44.84±3.17) μm, respectively. The thicknesses of Fe-Al alloy layers are (150.37±4.95) μm and (138.08±6.05) μm, respectively. The bonding strength between aluminum coating and substrate prepared by hot dipping is approximately 163.90N, while that prepared by magnetron sputtering combining with hot dipping is 160.25N. The corrosion mass loss rates of hot dip aluminizing Q235 steel and magnetron sputtering combining with hot dip aluminizing Q235 steel are about 1/12-1/6 of that of uncoated sample, and the corrosion pits of the latter one are more uniform.

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    Effect of rotation speed on microstructure and properties of dissimilar submerged friction stir welding joints of aluminium and pure copper
    Ying-hui WANG, Kuai-she WANG, Wen WANG, Pai PENG, Qian-ying CHE, Ke QIAO
    2019, 47 (11): 155-162.   DOI: 10.11868/j.issn.1001-4381.2018.000446
    Abstract ( 477 ( PDF (6984KB)( 213 Citation

    2024-T4 aluminium alloy and pure copper were welded by submerged friction stir welding (SFSW) and the effect of rotation speed on microstructure and mechanical properties of SFSW joints was studied. The results indicate that the SFSW joint is well formed, without cracks, holes and other defects. With the increase of rotation speed, the surface of the SFSW joint is smooth and the smoothness is improved. Meanwhile a large number of copper is involved in the nugget zone (NZ), and the structure in NZ is gradually disordered; the forced cooling effect of water effectively inhibits the formation of grain coarsening and brittle intermetallic compound during SFSW; the tensile strength of joint is 227MPa, which is 70.3% of the tensile strength of the copper base metal(BM) at the rotational speed of 750r/min and the tensile strength and elongation of the SFSW joint decrease with the increase of rotation speed.

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    Quantitative study of superplastic deformation mechanism of 5A90 Al-Li alloy
    Ling-ying YE, Dong YANG, Hong-ping LI, Xin-ming ZHANG, Rong-yue LIAO
    2019, 47 (11): 163-170.   DOI: 10.11868/j.issn.1001-4381.2018.000326
    Abstract ( 467 ( PDF (5513KB)( 198 Citation

    The contribution of grain boundary sliding(GBS) and intragranular dislocation slip(IDS) in the 5A90 Al-Li alloy during superplastic deformation at 480℃ and an initial strain rate of 1×10-3s-1 was quantitatively investigated by analyzing the deformation-induced changes in the sample surface having micron grids etched by focused ion beam. As supporting evidence, scanning electron microscope and electron back scattering diffraction were used to analyze the microstructure evolution during superplastic deformation. The results show that superplasticity is the result primarily contributed by intragranular dislocation slip(about 60%-80%)in the first stage(ε < 0.65) and grain rotation is coordination mechanism, with the banded grains refined and equiaxed and the average grain size decreased(about 40%). With the increase of strain, obvious dynamic recrystallization occurs, which gives rise to the increasing grain size, and decreased effect of intragranular dislocation slip, grain boundary sliding gradually becomes the main mechanism.

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    Small fatigue crack growth behavior of TB6 titanium alloy
    Liang XU, Shuang-jun HUANG, Li HUI, Lei WANG, Song ZHOU, Qing ZHAO
    2019, 47 (11): 171-177.   DOI: 10.11868/j.issn.1001-4381.2016.000866
    Abstract ( 653 ( PDF (4174KB)( 202 Citation

    The growth behavior of naturally-initiated small cracks in single edge notched tensile (SENT) specimen of TB6 titanium alloy was studied. Fatigue experiments were conducted under constant amplitude loading with the stress ratios R of 0.1 and 0.5 at room temperature. Small cracks were allowed to be monitored by replica method during fatigue testing. Results show that at the same stress ratio, the initiation life of crack increases from 60% to 80% of the total fatigue life with the decrease of stress level. However, the stress level has no significant effect on the crack growth rate of TB6 titanium alloy. The crack growth rate at the early stage is greatly affected by the microstructure. Once the crack length reaches 200μm, the crack growth rate will increase rapidly regardless of grain boundary or grain orientation. Small cracks of TB6 titanium alloy are originated from the sample notch root in the form of corner crack, and the major part of total fatigue life is consumed in small fatigue crack initiation phase.

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